document updated 12 years ago, on Jun 8, 2012

How does Bash determine true/false?

Bash itself (without using test) only uses a program's exit status. Zero ⇒ true, non-zero ⇒ false.

For example:

# is the given file a Perl script?
if perl -ne 'exit 0 if /^#!.*perl\b/; exit 1' $1; then
    echo "yes, $1 is a Perl script"
fi

details here